Fertilin, originally named PH-30, is a heterodimeric cell-surface protein identified on guinea pig, rabbit and human spermatozoa. The A-subunit has a 22 amino-acid hydrophobic peptide that is known to act as a "fusion peptide" during sperm-egg fusion. The mature fertilin B subunit has an amino-terminal 90-93 amino-acid domain With sequence homology to a class of known integrin ligands (the snake venom disintegrins), and it is suggested that this domain plays a pivotal role in sperm-egg binding as an integrin-disintegrin interaction. Based on these observations, fertilin and the egg receptor for fertilin could be a potential target for contraception. Some scientists have explored the possibility of using purified fertilin as an antigen for immuno-contraception. Three male guinea pigs received injections of fertilin; studies showed that 100% of the males were infertile. Several control males received injections of adjuvent without protein and none of them were infertile. Other studies showed that fertilin B is expressed only in testis of humans. We plan to design a NH2 terminal 93 amino-acid fragment of human fertilin B (fertilin B-NTP93) containing integrin-disintegrin binding domain to be used as an antigen. Eventually, we plan to determine the inhibiting ability of sperm-egg binding by anti-human fertilin B-NTP93 antibody in vitro.